Double block and bleed valves are commonly used in the oil and gas industry. Also known as a DBB plug valves, the DBB valve provides the ability to simultaneously block upstream and downstream flows while also providing the ability to bleed off fluid from the downstream side of the valve. Commonly used in a variety of applications, the DBB valve is an effective mechanism for isolating or blocking fluid flow through a system.
As known to those skilled in the art, a DBB valve includes a valve body and a rotatable plug such as depicted in FIGS. 1-2. Rotation of the plug from a first closed position to a second open position allows for fluid flow through the valve by aligning a central passage in the plug with the inlet and outlet of the valve. As depicted in FIGS. 1-2, when in the open position, the dimensions of the plug closely conform to the interior of the valve thereby providing efficient flow through the plug with little to no fluid loss to the interior of the valve. As known to those skilled in the art, slips (not shown) carrying resilient seals retract away from the valve body as the plug transitions from the closed to the open configuration. With the plug in the open position, rotation of the hand wheel will close the valve by rotating the plug and moving the plug downward resulting in obstruction of the valve body by the plug and outwardly expanding slips carried by the plug. The slips force the resilient seal against the valve body over the inlet and outlet thereby providing a positive closure of the valve to fluid flow. In order to accommodate the downward movement of the plug, the design of the valve body requires a cavity beneath the plug. Over time, the cavity fills with sediment, debris or sludge. The buildup of sediment, debris or sludge in the cavity will eventually preclude smooth operation of the valve and may lead to failure of the valve.